1. Field of the Invention
The present invention relates broadly to frequency translators and methods for translating a radio frequency (RF) signal between a first frequency band and a second frequency band. More particularly, the present invention concerns a frequency transverter and method for enabling bi-frequency dual-directional transfer of digitally encoded data on an RF carrier by translating between a first frequency band, such as the 2.4 GHz ISM band, and a second frequency band, such as the 5.0 GHz-6.0 GHz U-NII band.
2. Description of the Prior Art
Developments in a number of different digital technologies have greatly increased the need to transfer large amounts of data from one network or system to another. As a result, the 900 MHz and 2.4 GHz unlicensed frequencies are becoming increasingly overcrowded and congested. This is exacerbated by the fact that only three of the twelve DSSS channels assigned in the 2.4 GHz ISM band are usable simultaneously at 11 Mbps within a 1000 foot radius using an omni-directional antenna. Thus, fixed wireless local area networks (LANs), for example, involving digitally encoded data modulated onto an RF carrier signal in the 2.4 GHz ISM band, suffer increasing interference from a variety of devices, such as, for example, microwave ovens, cordless telephones, and Bluetooth apparatuses.
One solution to such overcrowding is to use a prior art frequency translator to translate the RF carrier signal between the 2.4 GHz ISM band and a second unlicensed band, such as, for example, the Unlicensed National Information Infrastructure (U-NII) band, thereby avoiding the congestion and interference. Certain sub-bands of the U-NII band are currently used primarily by U.S. government operations, particularly military radar operations. Other sub-bands are used as follows: 5.00-5.25 GHz is allocated on a primary basis to the aeronautical radionavigation, aeronautical mobile-satellite (R), fixed satellite and inter-satellite services for both government and non-government operations; 5.25-5.35 GHz is allocated on a secondary basis to the non-government radiolocation service; 5.650-5.925 GHz is allocated on a secondary basis to the amateur service; 5.725-5.875 GHz is designated for ISM applications and unlicensed Part 15 devices (radiocommunication services operating within this frequency range must accept harmful interference that may be caused by ISM applications); and 5.850-5.925 GHz is allocated on a primary basis to the fixed-satellite (Earth-to-space) service for non-government operations and to the radiolocation service for government operations.
Translating between the ISM and U-NII bands would facilitate, for example, connections among computers, televisions, appliance automation products, and on-premises network cable or telephone company access points within homes, schools, and health care facilities. Furthermore, recent technological developments now permit digitization and compression of large amounts of voice, video, imaging, and data information so as to allow for its rapid transmission from computers and other digital equipment within the network. Unfortunately, the ISM band is insufficient to allow for wireless transmission of this information within and among these networks. Translating these signals to the U-NII band, however, provides an immediate solution which accommodates existing WLAN and other legacy systems and allows for higher output powers.
Unfortunately, prior art frequency translators suffer from a number of problems and disadvantages, including, for example, that they are typically only two-terminal devices and require a different antenna for each frequency band. Furthermore, though the FCC precludes transmission at both frequency bands simultaneously, no provision is made to maintain a connection at the originating frequency. Additionally, up/down translation in prior art frequency translators between the first and second frequency bands can result in a phase noise which is undesirably higher than that of the signal's source, and can result in substantial undesirable spurious products. Additionally, it is well known that multipath levels cause increasing signal deterioration with increasing data rate, particularly at data rates of 10 Mb/s or greater. Thus, translating to 5 GHz using a prior art frequency translator results in an increase in propagation path loss which could degrade BER performance. Additionally, they typically do not accommodate or facilitate legacy systems. Yet another problem encountered when using prior art frequency translators involves potential interference resulting from band-sharing with other non-licensed services. Additionally, they are typically packaged undesirably near their RF or power source and away from the output antennas. Additionally, the circuitry of prior art frequency translators is typically constructed using a generic FR-4 PCB material which is undesirably lossy at 6 GHz, making it unsuitable for use in a U-NII band frequency translator.
Due to the above-identified and other problems and disadvantages in the art, a need exists for an improved frequency translator.